1. Field of the Invention
Embodiments of the present invention may relate to a method for controlling power of radio links. More particularly, embodiments of the present invention may relate to a method for efficiently deciding and combining transmit power control (TPC) commands from different radio links.
2. Background of Related Art
A Universal Mobile Terrestrial System (UMTS) is a third generation mobile communication system (IMT-2000) developed from a global system for mobile communications (GSM). The UMTS is intended to provide more improved mobile communication services on the basis of a GSM core network and Wideband Code Division Multiple Access (WCDMA). In December, 1998, the ETSI in Europe, the ARIB/TTC in Japan, the TI in the USA and the TTA in Korea organized the third generation partnership project (3GPP), and attempted to make detailed specifications of the UMTS.
For the fast and efficient technical developments of the UMTS, the 3GPP divides the standardization works of the UMTS into five technical specification groups (TSG) in consideration of network components and operation independency of the components. Each of the TSG develops, approves and manages specifications in the related areas. The TSG for the radio access network (TSG-RAN) develops the specification of functions, requirements and interfaces of a Universal Mobile Telecommunications Network Terrestrial Radio Access Network (UTRAN), which is a new RAN for supporting the WCDMA in the UMTS.
The TSG-RAN is composed of a plenary group and four working groups. A first working group WG1 relates to the specification of a physical layer (first layer), and a second working group WG2 relates to functions of a data link layer (second layer) and a network layer (third layer). A third working group relates to interfaces between a base station, a radio network controller (RNC) and a core network in the UTRAN. A fourth working group relates to requirements for radio link performance and items for managing radio resources.
FIG. 1 is a structure diagram illustrating a radio access protocol between a terminal (operated based on the 3GPP RAN specification) and a UTRAN. As shown in FIG. 1, the radio access interface protocol includes a physical layer (PHY), a data link layer and a network layer, and is divided into a control plane for transmitting a control signal and a user plane for transmitting data information. The user plane is an area for transmitting traffic information of a user such as voice or IP packets, and the control plane is an area for transmitting control information for maintaining a network interface or call. The plane may be divided into the user plane and the control plane to efficiently manage various traffics.
The protocol layer can be divided into a first layer Layer 1, a second layer Layer 2 and a third layer Layer 3 on the basis of three lower layers of an open system interconnection (OSI) standard model that is well known in the art of communication systems.
In the three layers, the first layer is operated as a physical layer for radio interface, and is connected to a medium access control (MAC) layer through at least one transmission channel. The first layer (or physical layer) performs coding, modulation, spreading and interleaving processes, and transmits or receives a primitive to be easily processed in the upper layer. The primitive used to display mutual interactions implies software type parameter transmission.
The primitive between the physical layer and the MAC layer is divided into a request primitive and an indication primitive. In general, ‘Request’ is a primitive transmitted from the upper layer to the lower layer, and ‘Indication’ is a primitive transmitted from the lower layer to the upper layer.
The primitive transmitted from the physical layer to the MAC layer is divided into forward channel information and backward channel information according to its channel information. A forward channel is an information channel transmitted from a base station to a terminal and is the channel that first receives information among the physical layers, and transmits the information to the upper layers. A backward channel is an information channel transmitted from the terminal to the base station.
FIG. 2 is a structure diagram illustrating a downlink dedicated physical channel (DPCH) frame. A dedicated channel and a common channel can be distinguished by whether only one subscriber can use one resource at a given point of time. For example, the channel used in a traffic status is regarded as the dedicated channel.
The DPCH is one of the information channels and will now be explained with reference to FIG. 2. The DPCH is divided into a dedicated physical control channel (DPCCH) and a dedicated physical data channel (DPDCH). The DPCCH is a channel for transmitting control information generated in the first layer, and the DPDCH is a channel for transmitting data information of the user. The two channels are time-multiplexed in one physical channel. An uplink DPCCH and an uplink DPDCH serve to carry a dedicated channel transmission channel.
On the other hand, a TPC command is one of the fields of the DPCCH and that experiences the same downlink channel as a common pilot channel (CPICH). Accordingly, if quality of the CPICH is deteriorated, then quality of the DPCCH is also reduced. As a result, reliability of the demodulated TPC command decreases. If the less reliable TPC command is used, then uplink power control may be badly performed. This may have detrimental effects.
In this regard, the 3GPP TS 25.214 V3.7.0(2001-06) 5.1 describes uplink power control for controlling the transmit power of the terminal. In 5.1.2.2.2 and 5.1.2.2.3, the uplink power control for controlling the transmit power of the terminal is divided into algorithm 1 and algorithm 2. Here, the specification suggests conditions that must be satisfied according to a method for combining TPC commands from radio links of different radio link sets in a process for performing uplink power control in soft handover. The contents relating to combination of the TPC commands from the radio links of the different radio link sets are suggested in the 3GPP TS 25.214 V3.7.0(2001-06) 5.1.2.2.2.3 and are summarized as follows.
The terminal must perform soft symbol decision Wi on power control commands TPCi from each radio link (i=1, 2, . . . , N, where N is a number of the TPC commands from radio links of different radio link sets). That is, the terminal must decide TPC_cmd, which is a combined TPC command, as represented by the following γ function:TPC_cmd=γ(W1,W2, . . . ,WN)
Here, TPC_cmd has a value of 1 or −1.
The γ function must satisfy the following conditions. When the TPC commands from the whole radio link sets have a reliable value of 1, then the output of the γ function becomes 1. When the TPC command from any of the radio link sets has a reliable value of 0, then the output of the γ function becomes −1.
As described above, the method for combining the TPC commands from each radio link in the process for performing the uplink power control in the soft handover is described in the specification. However, this specification only suggests the conditions that must be satisfied for the γ function. The specification does not teach or suggest actual embodiments, which makes it difficult to decide embodiment techniques. Accordingly, there are demands for techniques for reliably deciding and combining TPC commands under the given conditions of the specification.